1. Field of the Invention
The present invention relates to an image forming apparatus of the type which forms an image either in a first exposure mode in which an original document circulated by a document recirculation means is stationed on a document table while an exposure means is moved to expose and scan the original document or a second exposure mode in which an original document is moved across the document table by the document recirculating means while being exposed and scanned by a stationary exposure means. More specifically, the present invention is concerned with an image forming apparatus of the type described, wherein recording medium sheets having images formed thereon are stored in a storage means having a plurality of storage sections.
2. Description of the Related Arts
Image forming apparatuses have been proposed which selectively operate either in "document-fix" reading mode or in "document-move" reading mode. The term "document-fix mode" is used to mean an image forming operation mode in which a plurality of document sheets fed by a recirculation type document feeder are successively placed on suitable portions of a platen, and are fixed while an image reading means in the apparatus is moved to scan and read the images of these document sheets. The "document-move" mode is a mode in which the image reading means is stationed at a suitable position, and is kept stationary while document sheets are successively fed by the recirculation type document feeder so as to move relative to the image reading means so that the images on the document sheets are read during movement of the document sheets.
In the known image forming apparatuses of the kind described, the document-move reading mode is employed for the purpose of realizing high-speed and stable reading of the original image, as well as image formation, particularly in a 1 to 1 copying operation where a single copy is produced from each original document sheet. When the document-move reading mode is used, it is possible to obtain a high image productivity, e.g., 100% or higher, by shortening the interval between sheets in the image forming apparatus. The document-fix reading mode, however, is advantageously employed in the so-called 1 to N fashion, i.e., when plural (N) copies are to be produced from a single document sheet, and, in particular, where stacking of sheets carrying the same image is required. When this mode is used, the productivity is 100% at the greatest. In order to increase the image forming speed per unit time, it is necessary to enhance the process speed of the image forming apparatus and the speed of circulating the original document sheets. This naturally leads to difficulties or problems such as necessity for motors having greater capacities and structure having higher rigidity, as well as problems from a rise in the noise level and a reduction in the reliability of the document feeding operation.